Reference is made to applicant's U.S. Pat. No. 3,738,370 which discloses the use of a coaxial cable catheter for placing electrodes in or near the heart using a transvenous technique. A sensor is provided to detect a fibrillation condition, and in response to such detection electrical energy is supplied through the coaxial cable to the electrodes to effect defibrillation. The entire disclosure of such patent hereby is incorporated by reference.
The terms defibrillation and cardioversion are used interchangeably and equivalently herein. It is, of course, known that both defibrillation and cardioversion apply electrical signals for overcoming a fibrillation or arrythmia condition. A primary difference between defibrillation and cardioversion is that in the latter a synchronization function is imposed to synchronize the applied shock with a particular signal detected from the heart.
The use of electrical energy to effect defibrillation of a heart has been known for some time. In addition to the bi-polar coaxial cable catheter approach previously disclosed by applicant in such patent, the application of electrical energy to the exterior of a patient's body, e.g. using a pair of conductive paddles, is one prior technique. Another technique is that in which one electrode is implanted using a transvenous path to the heart and a second electrode is surgically implanted in the chest cavity outside the heart. In all case it is desirable to provide adequate electrical energy or an electrical input of a particular characteristic that is adequately large, such as current or voltage, to effect defibrillation without damaging the heart or a part thereof.
One disadvantage to the "paddle" technique is that the equipment is not particularly portable, certainly not implantable, and another disadvantage is the relatively large amount of electrical energy required to effect defibrillation due to the impedance, for example 100 ohms, of the patient's body. The prior combination transvenous electrode and surgically implanted electrode technique requires less energy than the "paddle" technique for defibrillation, e.g. due to the reduced, about 50 ohms, impedance of the "exposed" heart; but the fact that surgical implantation is required itself is disadvantageous.
Various types of electrical signals (as used herein "electrical signals" means the actual electrical power or energy delivered for effecting defibrillation unless otherwise apparent from context) have been used for defibrillation. Examples include square wave forms, trapezoidal wave forms, wave forms derived from capacitor discharge through resistive impedance, wave forms derived from delay line coupling systems, and so on. Reference is made to the publication "Servicing Medical And Bioelectronic Equipment" by J. Carr, published by the George Washington University, February, 1977, pages 148-165, where a description of a Lown wave signal and circuitry for obtaining the same are presented. The entire disclosure of such publication hereby is incorporated by reference.
Also, various types of sensors may be used to detect a fibrillation condition to trigger operation of defibrillation equipment. Exemplary sensors and operating detector circuits for defibrillation equipment are disclosed in U.S. Pat. Nos. 4,184,493, 4,270,549, 4,393,877, and 4,559,546, the disclosures of which hereby are incorporated by reference.